Control means for a fluid-powered device

ABSTRACT

Fluid control means, employing a pair of valving members, to automatically cycle the operation of the device. One valving member is translated in one direction, as the device is fluidcharged, to a point at which said one valving member opens fluid passages to a triggering chamber to fire the device. The second valving member holds the triggering chamber open to venting, to drain leak-through fluid, until the device is about to fire. Then, just prior to the firing, the first valving member opens passages to pressured fluid which drives the second valving member into closure of vent passages to halt the venting of the triggering chamber. Firing of the device returns the first valving member in the alternate direction for re-charging of the device.

Dec. 9, 1975 CONTROL MEANS FOR A FLUID-POWERED DEVICE Jack B. Ottestad, La Jolla, Calif.

Impulse Products Corporation, San Diego, Calif.

Filed: Mar. '1, 1974 Appl. No.: 447,083

Related US. Application Data Division of Ser. No. 279,694, Aug. 10, 1972, Pat. No. 3,822,633.

Inventor:

Assignee:

US. Cl. 91/224; 9l/235; 91/268; 9l/272 Int. Cl. F01B 11/00; FOlL 15/16 Field of Search 9l/222, 224, 235, 268, 91/272, 321, 422, 442

References Cited UNITED STATES PATENTS l/l968 Ottestad 91/5 3,524,385 8/l970 Ottestad 91/235 X Primary Examiner-lrwin C. Cohen Attorney, Agent, or Firm-Bemard J. Murphy [57] ABSTRACT Fluid control means, employing a pair of valving members, to automatically cycle the operation of the device. One valving member is translated in one direction, as the device is fluid-charged, to a point at which said one valving member opens fluid passages to a triggering chamber to fire the device. The second valving member holds the triggering chamber open to venting, to drain leak-through fluid, until the device is about to fire. Then, just prior to the firing, the first valving member opens passages to pressured fluid which drives the second valving member into closure of vent passages to halt the venting of the triggering chamber. Firing of the device returns the first valving member in the alternate direction for re-charging of the device.

4 Claims, 10 Drawing Figures U.S. Patent Dec. 9 1975 Sheet2 0f4 3,924,513

FIG. /A

US. Patent Dec. 9 1975 Sheet 3 of4 3,924,513

Sheet4 of4 3,924,513

US. Patent Dec. 9 1975 CONTROL MEANS FOR A FLUID-POWERED DEVICE This is a division of application Ser. No. 279,694 filed Aug. 10, 1972, now US. Pat. No. 3,822,633.

This invention pertains to control means for fluid powered devices and in particular to such control means which effect automatic recycling of such devices.

In the prior art, expecially from my earlier U.S. Pat. No. 3,363,513 issued Jan. 16, 1968, entitled Impact Ram, are disclosed means external of the device for effecting manual recycling. In a subsequent US. Pat. No. 3,524,385, issued Aug. 18, 1970 for Control Means for a Fluid Powered Device, I set forth means wholly confined within the device for effecting automatic recycling of the device. The instant invention constitutes an improvement of these prior teachings for control means for effecting automatic recycling of a fluid powered device such as an impact ram or the like.

By way of example, the device contemplated for use with my novel control means, such as an impact ram device, typically comprises a housing in which a plunger is slidably disposed therewithin, the piston and hollow plunger cooperating with an end of the device to define therewithin a chamber for confining a gas. The housing is ported for admitting and venting fluid, such as hydraulic fluid into and from the housing, and the housing, piston and plunger cooperate to define both a charging chamber and a triggering chamber.

As described in my more recent U.S. Pat. No. 3,524,385, (cited herein) the hydraulic fluid is admitted to the charging chamber to cause the piston to retract within the plunger to compress the gas. The triggering chamber is provided for subsequently receiving the charge of pressured hydraulic fluid to admit the pressured fluid to an end surface of the plunger, so that the device is fired by causing the plunger to accelerate in a given direction. To insure proper and repetitive firing of the device, valving means is provided within the device either integral with the piston, or separate therefrom, to hold the triggering chamber closed off from venting until the device is fired. Subsequently the valving means automatically admits the fluid charge into the triggering chamber for impingement thereof upon the plunger surface. Only thereafter, the valving means vents the triggering chamber. In summary then, according to my earlier teaching, the device-recycling valving means hold the triggering chamber closed to venting all the while the device is being fluid-charged, and opens the triggering chamber to venting only after the device has fired.

This prior teaching of my control means is reasonably effective. However, it necessitates stringent manufacturing control of mating parts to insure that there will not be a leakage of fluid into the triggering chamber which will cause a misfire, a precipitate firing, of the plunger. In the present invention I teach means for overcoming this limitation, and make it possible for manufacturing tolerances, and clearances of the mating components to be met with relaxed standards. It is an object of this invention, therefore, to teach control means for a fluid-powered device, such as an impact ram or the like, wherein the device has a working plunger, and a housing supporting the plunger for movement, said housing having a surface cooperating with a surface of said plunger to define a triggering chamber therebetween, and including means for admitting pressured fluid into said housing and means for venting fluid from said housing; comprising valving means within said'housing operative in response to an admittance of pressured fluid into said housing to cause a portion of said housing to become charged to a predetermined level with said pressured fluid, operative to hold said triggering chamber open to venting via said venting means, until said predetermined level is reached, and operative to close off said triggering chamber venting and to direct pressured fluid from said housing portion into said triggering chamber, when said predetermined level is reached, to cause movement of said plunger.

A feature of this invention comprises fluid control means employing a pair of valving members to automatically cycle the operation of the device. One valving member is translated in one direction, as the device is fluid-charged, to a point at which said one valving member opens fluid passages to a triggering chamber to fire the device. The second valving member holds the triggering chamber open to venting, to drain leakthrough fluid, until the device is about to fire. Then,

' just prior to the firing, the first valving member opens passages to pressured fluid which drives the second valving member into closure of vent passages to halt the venting of the triggering chamber. Firing of the device returns the first valving member in the alternate direction for re-charging of the device.

Further objects and features of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying figures, in which:

FIG. 1 is an axial cross-sectional view of a first embodiment of the invention; & FIG. 1A is a detail thereof.

FIG. 2 is a partial cross-sectional view taken from FIG. 1 showing the device in a first operative position;

FIG. 3 is a partial view corresponding to that of FIG. 2 showing the device in a second operative position;

FIG. 4 is an axial half cross-sectional view and half external view of an alternate embodiment of the invention; 1

FIGS. 5 and 4 depict details of the means which supply pressured fluid into the end cap assembly for charging of the device (of FIG. 4); and means for draining the fluid from the device;

FIG. 6 is a partial, axial, half cross-sectional view and half external view of the'FIG. 4 embodiment valving arrangement which effects recycling of this embodiment of the device, according to the invention; and

FIGS. 7-9 depict operational functioning of the seal base pins of the FIG. 1 embodiment of the invention.

In FIG. 1 is shown a fluid-powered device 10, the same being an impact ram, which incorporates the control means 12 of the invention. The device 10 comprises a housing 14in which a hollow plunger 16 is slidably received, the plunger confining therewithin a piston 18 which defines an inner chamber 20 of the plunger. The chamber 20 receives a charge of gas, via a port 22 and fitting 24, for resiliently constraining the piston 18 in the illustrated direction within the plunger 16. One end 26 of the piston is matingly received by an orifice 28 which is carried by an orifice retainer 30. The retainer 30 has a surface 32 which defines a triggering surface for the plunger 16. This surface 32 cooperates with the end cap assembly 34 of the device to define a triggering chamber 36.

The piston 18 has a probe 38 ext'endingtherefrom which makes a substantially-sealed, sliding'fit within a bore 40 formed withina seal base 42 which is coupled to the end cap assembly 34. An orifice seat 44 is disposed betweenthe seal base 42 and orifice 28. The seal base has a recess 46 in an end thereof to receive a poppet 48, the poppet and piston probe 38 being concentrically assembled. Vent channels 50 and a vent chamber 52 formed in the end cap assembly 34 open onto a vent port 54 which communicates with a fluid reservoir (not shown). The poppet 48 has a conical terminal 56 which opens or closes off the vent channels 50, whereby the triggering chamber 36 is permitted to open onto the reservoir or is closed off from venting The seal base 42 has a second recess 58 in which is received a skirt 60 of the poppet 48. An annular limit stop member 61 is set within recess 46.

The seal base '42 has a pair of triggering ports 62 formed therethrough which open internally of the seal base, onto recess 58, and open externally onto the triggering chamber 36. Finally, the piston probe 38 is hollow substantially throughout the length thereof and has a' pair of lateral ports 64 adjacent the terminal end thereof for purposes to be explained hereafter.

As more fully described in my prior, cited patents, pressured hydraulic fluid is admitted by way of a housing fluid inlet port 66 to communicate with a return chamber 68 defined between the plunger 16 and the housing 14 for subsequent admittance through a plunger fluid inlet port 71) and therefrom into the charging chamber 72 of the device. The charging chamber 72 is defined by the outer surface of piston end 26, and surfacing presented by the seal base 43, the orifice seat 44 and the orifice 28.

It does occur that there is some leakage of hydraulic fluid between the orifice seat 44 and the orifice 28; this leakage fluid is free to vent throught the vent channels 50, passing through the triggering chamber 36 without causing a firing of the device 10. So also, there is leakage between the piston probe 38 and the seal base 42; this fluid too is .free to pass through the triggering ports 62 and triggering chamber 36, without effecting the operation of the plunger 16, and will drain through the vent chamber 52. This novel fail-safe provisioning proceeds from the inventive arrangement of the poppet and vent chamber surfaces, and fluid pressures operative there, and elsewhere in the device, as explained below.

Poppet 48 is caused to withdraw from port 54, thus a precipitate build-up of fluid pressure in triggering chamber 36 cannot occur; the movement of poppet 48 into recess 58 holds the triggering chamber 36 open to venting. It is hydraulic fluid pressure which opens port 54, and holds it open all thewhile that the charging chamber 72 is being charged with fluid. Leakagehydraulic fluid, the same being at some pressure level, upon reaching the triggering chamber 36, can only open port 54. In chamber 36, the minimal quantity of moderately pressured leakage fluid cannot overcome the restraint of plunger 16, yet, poppet 48 presents a considerable impingement surface, in its conicalterminal 56, and must yield, and move into recess 58. Accordingly, the poppet 48 is always operative to hold the triggering chamber 36 open to venting all thewhile that the chamber 72 is being charged. 7

In normal operation, the pressured hydraulic fluid admitted via port 66 will cause the piston 18 to translate down through the plunger 16 to compress the gas 4 confined within chamber 20. The piston 18 continues to move, as the chamber 72 is being charged,-and all this while the poppet 48 is displaced from the port 54 in the end cap assembly 34, to provide for free venting of the triggering chamber 36, as just described. When the lateral ports 64 in the. piston probe 38 just clear the lowermost surface of the seal base 42, the pressured fluid in chamber 72 can pass through these ports 64 and out the hollow end of the probe 38 to effect two results. For one, the pressured fluid impinging upon a dome-shaped surface .74 of the poppet 48 causes the poppet to move into port 54 and close off the vent chamber. Additionally, the pressure fluid is admitted through the triggering ports 62 into the triggering chamber 36. Consequently, the triggering surface 32 of the plunger 16 receives the pressured fluid, and the plunger is driven on its working stroke.

These operations are depicted in FIGS. 2 and 3. In FIG. 2 is shown the charging of the chamber 72 and the partial translation of the piston 18 within the plunger 16. It is to be noted that the poppet 48 is displaced from the poppet seat in port 54, and the triggering chamber 36 is fully open to venting. In FIG. 3 the piston 18 has traveled most of its full distance; the lateral ports 64 have just cleared the lowermost surfaces of the seal base 42, and the highly pressured fluid within the charging chamber 72 can pass therethrough to seat the poppet 48 and close off the venting of the triggering chamber 36, and impinge on surface 32 to move the plunger 16 on its stroke.

FIG. 4 shows an alternate embodiment of the invention in which same or similar index numbers signify same or similar comonents. This embodiment is also incorporated in a device 10' having a housing 14 and a plunger 16 with an end cap assembly passage 78 for venting the pressure fluid from the device. FIGS. 5 and 4 illustrate the coupling of a drainage pipe 80 for removing the fluid from the vent passage 78, and the supply of pressured hydraulic fluid to a port 82 formed in the end cap assembly 34'. A pipe .84, carries the fluid to port 82, and a short channel 86 conducts the fluid to chamber 76. Passage 78 opens into a vent port 54' which receives a poppet 48.

In this embodiment it is the poppet 48 which has lateral ports 64 (only one is shown) for admitting the trig gering fluid pressure into the triggering chamber 36. The piston probe 38 in this embodiment is not hollow, neither is it drilled through with passageways. On the contrary, the poppet 48', the piston probe 38 and the seal base 42 each have relievedsurfaces 88, 90 and 92, respectively, formed therein, these surfaces being cooperative to define an annular passageway, about the piston probe 38, to communicate the charging chamber 72 with the ports 64 in the poppet 48 for admittance of the pressured fluid through the triggering ports 62 (only one is shown) formed in the seal base 42 to the triggering chamber 36'. The piston probe 38', poppet 48' and seal base 42 also have lands 96, 98 and 100, respectively, which cooperate to prevent the admittance of the pressured fluid into the triggering chamber 36' until the piston 18 has traveled a predetermined distance within theplunger l6.

In this embodiment, as in that of FIG. 1, the poppet 48 is displaced from the vent port 54 in the end cap assembly 34 all the while that the device is'charging. Again, this is to accommodate the venting. of leakthrou'gh fluid which passes between the orifice 28 and the seal base 42'; and between the piston probe 38 and the seal base 42 and poppet 48 prior to the piston 18' having traveled its full required distance. Shortly after land 96 has cleared the land 100 at the bottom of the seal base 42', the annular passageway is defined about the piston probe 38' and admits the fluid first to the poppet 48 to hold the poppet sealingly against the seat of port 54, to prevent any further venting of the triggering chamber 36. Then, also, the fluid further proceeds through the lateral ports 64 in the poppet 48 down throughthe seal base triggering ports 62 into the triggering chamber 36. There it impinges upon the orifice 28' to cause the plunger to be driven on a working stroke.

This second embodiment has additional features which greatly enhance the reliable operation thereof. For instance, the piston probe 38 has a second land 104 which, in the furthermost travel of the piston 18 seals with land 98 of the poppet 48'. Accordingly, as land 96 of the probe 38 clears the land 100 of the seal base 42, relieved surfaces 90 and 92 cooperate to direct the pressured fluid against the skirt 106 of the poppet 48. This first, and positively, drives the poppet 48' into closure of port 54. Also, poppet 48' carries an annular shoulder 108 which,'following the firing of the plunger 16 (when-the plunger proceeds to retract), re ceives the fluid pressure thereon from the fluid being evacuated from chamber 36' and this positively holds the poppet 48 away from the port 54'.

The retraction of the plunger 16 (or 16') and the re seating of the piston 18' (or 18), for a recharging of the device(s), is effected in thesame manner as described in detail in my priorly-issued patents.

With reference, for example, to the embodiment depicted in FIGS. 1, 1A, 2, 3, and 7-9, plunger retraction is explained. The plunger 16 will be in its furthermost extended position, and piston 18, under the urging of gas in chamber 20, will have returned to mating engagement with the orifice 28 (as seen in FIG. 7). The poppet 48 will be unseated from port 54, for two reasons. For one, the triggering charge, which both fired the plunger 16 and forced the poppet 48 to its seat, is spent; also, as the piston 18 rebounds under the force of the gas, it forces hydraulic fluid around the orifice seat 44 through the vent channels 50 to bear on the conical terminal 56 of the poppet 48. Thus, the poppet opens the port 54, and remains displaced from the port until another triggering force seats it again.

Pressured hydraulic fluid admitted via port 66 again operates on the under surfaces of the orifice 28 and retainer 30 to proceed to retract the plunger 16. All this while, the lateral ports 64 in probe 38, and the triggering ports 62 and triggering chamber 36 as well, are all open to venting. As the probe 38 never clears the seal base 42 it only withdraws far enough to allow ports 64 to open onto charging chamber 72 it cooperates with bore 40 to prevent premature hydraulicfluid charging of triggering chamber 36.

As discussed further on, in connection with FIGS. 7-9, the piston 18 first seals with the orifice 28, as the plunger 16 continues to retract, and then the plunger 16 seals with the orifice seat 44. As the plunger 16 is finally seating, becoming fully retracted, the piston 18 is displaced from the orifice 28; this is to expose an impingement surface of the piston 18 to cause it to yield to the incoming, pressured hydraulic fluid and to become charged again for the next stroke.

To insure a continuous recycling of the devices and 10', the depicted embodiments have features oper- 6 ative to prevent a high pressure stall from occuring. These features, with reference to FIGS. 1 and 8-9 for device 10, and FIG. 7 for device 10, are described in the following paragraphs.

Seal base 42 (FIGS. 1, 7-9) has a pair of pins 110 extending therefrom. Pins 110 are disposed for contacting the head of piston 18, upon the return of piston toward the seal base, and for holding the piston a specified distance away from orifice 28 as the orifice closes upon the orifice seat 44. This is necessary to be able to charge the device 10 for an onfollowing cycle, because of the geometry of the piston 18 and orifice 28.

The gas in chamber is operative against the full undersurface of the piston 18. Thus, if only a minimal, annular surface of piston 18 is exposed for impingement of hydraulic fluid thereon, the hydraulic fluid pressure would have to be inordinately high to overcome the bias of the gas pressure before the piston 18 could proceed to translate down through the plunger 16. Therefore, a cycle stall" would obtain, until the hydraulic pressure was sufficiently increased. Pins 1 l0 avoid this problem, and yet they accommodate a neces- ,sary, reasonable effective sealing-off of triggering chamber 36 from charging chamber 72 as the plunger 16 proceeds to seat in its retracted position.

As illustrated in FIG. 7, the piston 18 and plunger 16 are retracted from a preceeding firing of the device 10. A reasonably effective seal obtains at point A while both the piston 18 and plunger 16 move together toward the seal base 42.

In FIG. 8 is shown that operative progression where the following events proceed to occur: Pins 1 10 contact the head of piston 18, preventing further piston travel; seal point A proceeds to migrate away (downwardly) from its prior location; and a new, reasonably effective seal B proceeds to be joined between the orifice seat 44 and the orifice 28. Seal B is first located only at the lowermost extremity of orifice seat 44; as the plunger 16 continues to seat, seal B grows in depth along a short, axiallydisposed, annular interface of seat 44 and orifice 28.

FIG. 9 shows the piston 9 held off, by pins 110, from closure against orifice 28, providing access to the head of the piston 18 for the in-charging hydraulic fluid. Seal point A on piston 18 is displaced from the orifice 28, yet seal B is fully joined.

Device 10' (FIG. 4 and 6) relies on the geometry of piston 18' and seal base 42' to open the head of piston 18 to charging hydraulic fluid after plunger 16' has initiated a sealing between triggering chamber 36' and charging chamber 72. Piston 18' has an annular shoulder 112 which impinges against the lowermost surface of seal base 42 to prevent a closure of chamber 72' to the head of the piston. Yet, when the piston 18' and plunger 16' are retracted toward the seal base 42', a seal is maintained at A. This seal opens, but only after another seal B is commenced between the orifice 28' and the seal base 42', upon the shoulder 112 engaging the seal base, and as the orifice 28' fully closes upon the seal base.

While I have described my invention in connection with specific embodiments, thereof it is to be clearly understood that this is done only by way of example, and not as a limitation to the scope of my invention as set forth in the objects thereof, and in the appended claims.

I claim:

1. Control means for a cyclically operated fluid-powered device such as an impact ram or the like wherein the device has a working plunger, and a housing supporting the plunger for movement, said housing having a surface cooperating with a surface of said plunger to define a triggering chamber therebetween, and means for admitting pressured fluid into said housing including means for supplying admitted fluid to a portion of said plunger to hold said plunger against movement and means for venting fluid from said housing; comprising:

means within said housing defining a charging chamber for receiving pressured fluid and for being charged to a predetermined level with said pressured fluid; valving means operative to hold said triggering chamber open to venting via said venting means, until said predetermined level is reached, and operative, when said predetermined level is reached, to close off said triggering chamber venting and to direct pressured fluid from said charging chamber into said triggering chamber to cause movement of said plunger; wherein said valving means includes a wall member movably disposed within said housing, in slidable and sealing engagement with the plunger; and

means for resiliently and normally constraining said wall member in a given direction relative to said charging chamber; wherein said venting means comprises a fluid-conductive passageway open to venting at one end thereof, and opening into said triggering chamber at another end thereof;

said valving means further includes closure means movably disposed within said passageway to allow venting of said triggering chamber and for closing off triggering chamber venting;

said closure means and said wall member each having pressured-fluid-impingement reaction surfaces;

said wall member reaction surfaces being disposed to receive housing-admitting pressured fluid thereupon to effect a movement of said wall member in a direction other than said given direction; and

said wall member has probe means cooperative with said closure means and said housing to define a conduit for conducting pressured fluid from said close off said passageway to halt venting of said triggering chamber, wherein said wall member comprises a piston;

said probe means comprises an elongated probe, ex-

tending from and movable with said piston;

said housing has a bored-through seal base element fixed interpositionally between said charging member and said triggering chamber, and

said closure means has at least one triggering port formed therein communicating at one end thereof with said closure means reaction surface and in communication at the other end thereof with said triggering chamber.

2. Control means, according to claim 1, wherein:

said one triggering port opens at the one end thereof onto said piston and probe, and onto said venting means at the other end thereof;

said bore of said base element receives said probe and said closure means therewithin;

said probe closes off said bore of said base element, substantially to seal said charging chamber from said triggering chamber; andsaid probe, closure means, and base element have first surfaces, spaced apart one from the others thereof, which cooperate to define said conduit therebetween, upon said piston having moved said predetermined distance, and second surfaces which cooperate to close off said conduit upon said piston being displaced in said given direction.

3. Control means, according to claim 1, wherein:

said closure means comprises a hollow, walled popsaid one triggering port is formed in the wall of said P pp said'poppet wall has a raised, annular land formed thereon;

said probe has a plurality of spaced-apart, raised annular lands formed thereon; and

said lands of said probe, upon movement of said piston engage said poppet wall land to close off said triggering chamber from said charging chamber.

4. Control means, according to claim 3, wherein:

said poppet and said probe are concentrically disposed within said housing;

said probe is received within the walled hollow of said poppet; and

said wall of said poppet defines said reaction surfaces of said closure means, 

1. Control means for a cyclically operated fluid-powered device such as an impact ram or the like wherein the device has a working plunger, and a housing supporting the plunger for movement, said housing having a surface cooperating with a surface of said plunger to define a triggering chamber therebetween, and means for admitting pressured fluid into said housing including means for supplying admitted fluid to a portion of said plunger to hold said plunger against movement and means for venting fluid from said housing; comprising: means within said housing defining a charging chamber for receiving pressured fluid and for being charged to a predetermined level with said pressured fluid; valving means operative to hold said triggering chamber open to venting via said venting means, until said predetermined level is reached, and operative, when said predetermined level is reached, to close off said triggering chamber venting and to direct pressured fluid from said charging chamber into said triggering chamber to cause movement of said plunger; wherein said valving means includes a wall member movably disposed within said housing, in slidable and sealing engagement with the plunger; and means for resilientLy and normally constraining said wall member in a given direction relative to said charging chamber; wherein said venting means comprises a fluid-conductive passageway open to venting at one end thereof, and opening into said triggering chamber at another end thereof; said valving means further includes closure means movably disposed within said passageway to allow venting of said triggering chamber and for closing off triggering chamber venting; said closure means and said wall member each having pressuredfluid-impingement reaction surfaces; said wall member reaction surfaces being disposed to receive housing-admitting pressured fluid thereupon to effect a movement of said wall member in a direction other than said given direction; and said wall member has probe means cooperative with said closure means and said housing to define a conduit for conducting pressured fluid from said charging chamber to both said reaction surface of said closure means and to said triggering chamber, only upon said wall member having moved a predetermined distance in said other direction commensurate with said charging chamber reaching its predetermined level, to cause said closure means to close off said passageway to halt venting of said triggering chamber, wherein said wall member comprises a piston; said probe means comprises an elongated probe, extending from and movable with said piston; said housing has a bored-through seal base element fixed interpositionally between said charging member and said triggering chamber, and said closure means has at least one triggering port formed therein communicating at one end thereof with said closure means reaction surface and in communication at the other end thereof with said triggering chamber.
 2. Control means, according to claim 1, wherein: said one triggering port opens at the one end thereof onto said piston and probe, and onto said venting means at the other end thereof; said bore of said base element receives said probe and said closure means therewithin; said probe closes off said bore of said base element, substantially to seal said charging chamber from said triggering chamber; and said probe, closure means, and base element have first surfaces, spaced apart one from the others thereof, which cooperate to define said conduit therebetween, upon said piston having moved said predetermined distance, and second surfaces which cooperate to close off said conduit upon said piston being displaced in said given direction.
 3. Control means, according to claim 1, wherein: said closure means comprises a hollow, walled poppet; said one triggering port is formed in the wall of said poppet; said poppet wall has a raised, annular land formed thereon; said probe has a plurality of spaced-apart, raised annular lands formed thereon; and said lands of said probe, upon movement of said piston engage said poppet wall land to close off said triggering chamber from said charging chamber.
 4. Control means, according to claim 3, wherein: said poppet and said probe are concentrically disposed within said housing; said probe is received within the walled hollow of said poppet; and said wall of said poppet defines said reaction surfaces of said closure means. 